Cold Finger Test
What is it?
The principle of the Cold Finger instrument is an inverted pipeline. The cooled metal finger replicates the inner wall of a pipeline. The heated and stirred oil flows around it. When the finger’s temperature falls below the Wax Appearance Temperature (WAT), wax starts to deposit on its surface.
Why do we use it?
How does it work?
A cold finger is a piece of laboratory equipment that is used to generate a localized cold surface. It is named for its resemblance to a finger and is a type of cold trap. The device usually consists of a chamber that a coolant fluid (cold tap water, or perhaps something colder) can enter and leave. Another version involves filling the device with a cold material (examples: ice, dry ice or a mixture such as dry ice/acetone or ice/water).
Typically a cold finger is used in a sublimation apparatus, or can be used as a compact version of a condenser in either reflux reaction or distillation apparatus. Many commercially available rotary evaporators can be purchased with a cold finger in place of a Dimroth condenser, for example. When used as a condenser in a rotary evaporator, cold fingers can be cooled to a lower temperature of −78 °C (dry ice), compared with water condensers that can be cooled to −40 °C (ethylene glycol/water mixture). The lower temperature achieved reduces the quantity of volatile material exhausted into the air.